Anti-skid control system for motor vehicle

Abstract

An anti-skid control system for a motor vehicle, includes a brake fluid pressure buildup-control mode and a brake fluid pressure reduction mode, each of which occur cyclically. In each buildup-control mode, a control valve is repetitively opened and closed so that brake fluid pressure buildup and holding operations are performed alternately. The time period of each buildup-control mode is from a high peak of a wheel speed signal until a point of intersection between a reference velocity V W0 and the wheel speed V W . The reference velocity V W0 has an initial point Q positioned under the high peak V HP of the wheel speed V W by a velocity value ΔV and extending straight at a gradient θ. The speed value ΔV, the gradient θ, and an initial pressure buildup time T P , in each building-control mode, are determined in accordance with the wheel acceleration in the preceding wheel acceleration, i.e., coefficient of friction of the road surface.

We claim: 
     
       1. An anti-skid control system for a motor vehicle, including a brake fluid pressure buildup-control mode and a brake fluid pressure reduction mode, which occur in anti-skid cycles, said anti-skid control system comprising: first valve means for alternately building up and holding brake fluid pressure during said brake fluid pressure buildup-control mode;   wheel speed measuring means for measuring a speed of each wheel of the motor vehicle and for providing a wheel velocity signal V W  responsive to said speed;   peak detecting means for receiving said velocity signal V W  and for detecting a high peak value V HP  and a low peak value V LP  of said velocity signal V W  when said anti-skid control system is operated;   controller means for repetitively opening and closing said first valve means during said brake fluid pressure buildup-control mode, from a first time when said velocity signal V W  has said high peak value V HP  to a second time when said velocity signal V W  has a value R, said value R corresponding to said velocity signal V W  being equal to a reference velocity V WO  at the second time, said reference velocity V WO  having an initial value at the first time being less than said high peak value V HP  by a predetermined velocity value ΔV, having values which vary between the first time and the second time dependent upon a gradient θ, and having a final value equal to said velocity signal V W  at the second time corresponding to said value R;   acceleration measuring means for measuring wheel acceleration during a time after detection of said low peak value V LP  by said peak detecting means on the basis of said velocity signal V W  between a first value Va and a second value Vb of said velocity signal V W , said first value Va being dependent upon a predetermined rate of wheel velocity and said low peak value V LP , said second value Vb being dependent upon another predetermined rate of wheel velocity and said first value Va; and   determining means for determining at least one of said predetermined velocity value ΔV, said gradient θ and an initial pressure buildup time T P , for said brake fluid pressure buildup-control mode and in accordance with said measured wheel acceleration.   
     
     
       2. An anti-skid control system according to claim 1, wherein said predetermined velocity value ΔV, said gradient θ, and said initial pressure buildup time T P  are determined in accordance with said measured wheel acceleration in a preceding anti-skid cycle. 
     
     
       3. An anti-skid control system according to claim 1, wherein said acceleration determining means includes means for calculating a value R O  corresponding to said value R of a preceding anti-skid cycle, so that said first value Va and said second value Vb of said velocity signal V W  are defined as follows:   Va=K.sub.1 ([V.sub.WO ]R.sub.O -V.sub.LP)+V.sub.LP       Vb=K.sub.2 ([V.sub.WO ]R.sub.O -V.sub.LP)+V.sub.LP     where O<K 1  <K 2 .   
     
     
       4. An anti-skid control system according to claim 3, wherein K 1  =0.15 and K 2  =0.8. 
     
     
       5. An anti-skid control system according to claim 1, further comprising selection means for selecting said predetermined velocity value ΔV, said gradient θ, and said initial pressure buildup time T P  for an anti-skid cycle in accordance with a value of said measured wheel acceleration. 
     
     
       6. An anti-skid control system according to claim 1, wherein said acceleration determining means further includes: means for determining said first value V a  of said velocity signal V W  in accordance with a first predetermined value of velocity of said low peak value V LP  ; and   means for determining said second value V b  of said velocity signal V W  in accordance with a second predetermined value of velocity and said low peak value V LP .   
     
     
       7. An anti-skid control system for a motor vehicle, including a brake fluid pressure buildup-control mode and a brake fluid pressure reduction mode, each of which occurs in anti-skid cycles, said anti-skid brake control system comprising: first valve means for alternately building-up and holding brake fluid pressure during said brake fluid pressure buildup-control mode;   second valve means for reducing brake fluid pressure during said brake fluid pressure reduction mode;   wheel speed measuring means for measuring a speed of each wheel of the motor vehicle and for providing a wheel velocity signal V W  responsive to said speed;   peak detecting means for receiving said velocity signal V W  and for determining a high peak value V HP  and a low peak value V LP  of said velocity signal V W  when a wheel is braked;   controller means for repetitively opening and closing said first valve means during said brake fluid pressure buildup-control mode, from a first time when said velocity signal V W  has said high peak value V HP  to a second time when said velocity signal V W  has a value R, said value R corresponding to said velocity signal V W  being equal to a reference velocity V WO  at the second time, said reference velocity V WO  having an initial value at the first time being less than said high peak value V HP  by a predetermined velocity value ΔV, having values which vary between the first time and the second time dependent upon a gradient, and having a final value equal to said velocity signal V W  at the second time corresponding to said value R;   acceleration measuring means for measuring wheel acceleration during a time after detection of said low peak value V LP  by said peak detecting means on the basis of said velocity signal V W  between a first value Va and a second value Vb of said velocity signal V W , said first value Va being dependent upon a predetermined rate of wheel velocity and said low peak value V LP , said second value Vb being dependent upon another predetermined rate of wheel velocity and said first value Va;   determining means for determining at least one of said predetermined velocity value ΔV, said gradient θ and an initial pressure buildup time T P , for said brake fluid pressure buildup-control mode in accordance with said measured wheel acceleration; and   reduction control means for controlling opening of said second valve means during said brake fluid pressure reduction mode, from a time corresponding to an occurrence of said value R until a time corresponding to an occurrence of said low peak value V LP  of said velocity signal V W .   
     
     
       8. An anti-skid control system according to claim 7, wherein said acceleration determining means further includes: means for determining said first value V a  of said velocity signal V W  in accordance with a first predetermined value of velocity; and   means for determining said second value V b  of said velocity signal V W  in accordance with a second predetermined value of velocity.